The present invention relates to Josephson tunnel junction devices and more particularly to the use of Josephson tunnel junction devices in resonant circuits to provide automatic variance of the quality factor Q of the circuits.
The properties of various materials having particle systems with magnetic moments can conveniently be studied by methods such as nuclear magnetic resonance (NMR), electron spin resonance (ESR), nuclear quadrupole resonance (NQR), and similar systems. In general, a gyromagnetic particle system is irradiated by a high frequency (rf or microwave) pulse of a frequency which matches the natural processional frequency of the particles. After the pulse is turned off, the processing magnetization of the gyromagnetic particles will generate voltage signals across a pick-up coil which are then detected by a resonant circuit tuned to the frequency of the resonating system. The detected signal will have a magnitude proportional to the number of resonant particles in the system.
In order to detect the very weak signals from the resonating particles, a high-Q pick-up coil is needed. However, the strong exciting high frequency pulse will also be detected by the high-Q resonant circuit, and the consequent ringing of the high-Q resonant circuit will predominate for an appreciable time, masking detection of the weak, short-lived signals from the excited particles.
Attempts have been made to provide Q-spoilers which will reduce the Q of a resonant circuit when desired, such as to reduce the ringing from an excitation pulse, and which will allow the resonant circuit to have a high Q at other times, so that weak signals may then be detected. For instance, back-to-back diodes provide some cut-off, but the inherent forward resistance will limit the desirable high-Q of the circuit. Further, most Q-spoilers are complicated and unduly load the circuits in which they are used.